1. Field of the Invention
This invention relates generally to a diode-pumped, solid state laser-based workstation for use in a variety of precision materials processing and machining applications, and more specifically, to a workstation employing a diode laser endpumped, q-switched, fiber-coupled, solid state laser which produces a pulsed laser beam for ablating, and hence making precision cuts in, the surface of the material.
2. Background of the Invention
Lasers have been used in a variety of materials processing and machining applications. Their primary advantage is that they provide a directed energy beam at high average power which can be focused to micron beam diameters, allowing unique materials processing applications to be developed, such as the using lasers for semiconductor memory repair via link blowing, or precision engraving applications.
A requirement of lasers used in these types of applications in that the laser deliver short, high energy pulses having a pulse width which is short compared to the thermal diffusion time of the material being processed. This is necessary so that the material will ablate from the surface, that is evaporate without melting, enabling the laser to make precise and accurate cuts on the surface of the material. In fact, laser pulse widths of 50 ns or lower are typically necessary to achieve material removal by ablation.
Solid state lasers are particularly advantageous in producing a pulsed beam output since they have a long excited state lifetime, and hence can store energy from the laser pump source and then release the energy over a short time period through a process called q-switching. To produce pulses having a short enough width for ablation, as is known, lasers having either a short cavity or high gain are required, since pulse width depends on the product of gain and cavity round trip time. However, solid state lasers used in the art are typically pumped with an arc lamp, which is a broadband source, and not particularly efficient in pumping a solid state laser since it will pump portions of the lasing medium which will not contribute to production of the output beam, and because it contains many different wavelengths which will not be absorbed by the laser medium. In fact, the arc lamp electrical efficiency is typically only about 0.5%. The net result is that the gain per unit length of the system will be low, necessitating that the laser material be relatively long so that enough lasing material will be present for the laser to achieve the necessary gain required and thus produce a short pulse width. For example, a cavity having a 1 foot length is typically required.
In addition, because the gain is so low, quite a bit of input power must be applied to produce a short pulse, necessitating in many instances that water cooling of the laser head take place to control heat dissipation, and also necessitating that the laser be coupled to a 230 VAC outlet to produce the several kilowatts of input power which must typically be supplied to achieve the requisite gain. Moreover, the large cavity length implies a large beam diameter which will require a large q-switch to produce the pulsed output necessary for ablation.
The turbulence of the water cooling is problematic for precision materials processing and machining. This is because noise will be introduced into the pulsed laser beam by coolant water turbulence, which will limit the precision of the cuts possible.
In addition, the high input power required will be problematic for the additional reason that the energy delivered by the laser at the short pulse width will be much too high for ablation and precision cuts, necessitating that the laser output be attenuated before impinging upon the material. Lower power arc-lamp pumped solid state lasers are not a possible solution to the attenuation problem since they will not produce the short pulse widths required for material ablation. The net result is that the pulse width/energy level combination required for successful material ablation is not achievable with conventional, arc-lamp pumped, q-switched, solid state lasers.
The combined impact of the long cavity length and large q-switch, the required 230 VAC hook-up, the water cooling of the laser, and the attenuation of the laser output, make the laser bulky and mechanically difficult to integrate into an optical system for downstream focusing, shaping, and directing of the beam which may be required, and also make the laser and system in which it is integrated unwieldy and lacking in portability.
The low electrical efficiency provides for a significant amount of heat dissipation in the laser head of the laser, necessitating that a cooling system be applied to the laser head. A problem for precision materials processing is that vibrations from the cooling system will be coupled to the laser head, causing the head to move, and resulting in less precise cuts.
Finally, the arc lamp in such a laser is coupled to the laser head, often necessitating that the laser head be aligned and readjusted every time the arc lamp is required or serviced.
Accordingly, it is an object of the present invention to provide a solid state laser for use in a workstation for high precision materials processing, which provides the proper pulse width/energy level combination for ablation, which provides for efficient pumping in a compact laser cavity, which eliminates the need for water cooling with the attendant water turbulence induced noise to the laser output beam, which is small, compact, and easily integrable into an optical system for downstream focusing and directing of the beam, and which decouples the vibrations of the cooling system of the pumping source from the laser head, enabling the laser to produce more precise cuts.